Thermal decomposition and leaching mechanisms of copper(II) oxalate (CuC₂O₄) raw material obtained from chalcopyrite concentrate

Abstract

A comprehensive understanding of the dissolution mechanisms of metal oxalates, both in their raw and thermally decomposed states, is critical for enhancing selective metal recovery in hydrometallurgical processes. The present study focuses on selective copper recovery from a CuC₂O₄-rich raw material obtained by leaching chalcopyrite concentrate with oxalic acid and hydrogen peroxide. The principal objective was to elucidate the dissolution behavior of low-solubility oxalate phases in various leaching media, before and after thermal decomposition. Leaching experiments were performed in two stages: (i) direct leaching of the raw material in HCl, HNO₃, H₂SO₄, and NH₃ solutions, and (ii) leaching after thermal decomposition at 200 – 400 ° C. Phase transformations and dissolution mechanisms were systematically characterized using XRD, FTIR, SEM-EDS, and TGA – DTA analyses. Direct leaching achieved 52.1% Cu dissolution in 5 M HCl and 46.5% in 3 M NH₃, whereas dissolution in H₂SO₄ and HNO₃ remained minimal due to the limited solubility of CuC₂O₄. Upon thermal treatment at 400 °C, CuC₂O₄ fully decomposed into oxide and sulfate phases (Cu₂O(SO₄), Cu₂O, and CuO). Under these conditions, leaching in 5 M NH₃ resulted in up to 90.3% Cu dissolution with high selectivity. Overall, the findings confirm that metal oxalates generated from concentrates can be effectively and selectively dissolved in suitable solvents following controlled thermal decomposition, providing a viable strategy for improving hydrometallurgical copper recovery.

Keywords

chalcopyrite concentrate / copper (II) oxalate / thermal decomposition / selective leaching

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